It will be appreciated that the invention has utility with respect to improvements in electronic packaging that may be suitable for many applications. However, the present invention has some unique features which maximize utilization of space within an implantable medical device and provide enhanced protection for internal electronic components.
Implantable medical devices of the type having electrical circuit components are well known in the medical arts. In one particularly common form, the implantable device comprises a pacemaker, or other stimulation device, having an appropriate electrical power supply and related control circuitry for use in electrically stimulating a patient muscle, such as the heart. Such a pacemaker commonly includes a hermetically sealed case or housing within which a power supply and control circuitry are placed, in combination with one or more conductive pacemaker leads extending from the housing to the selected muscle structure within the patient.
Signals into and out of the circuitry within the housing of a common stimulation device are coupled through the housing by means of feedthrough terminals of various types known in the art. Examples of such stimulation devices may be found in commonly assigned U.S. Pat. No. 5,282,841 to Szyszkowski.
As is apparent from the Szyszkowski patent, the size of the housing is dependent upon that required to house both the battery and the electronic control circuitry constituting the pulse generator. A major factor which drives the electronic control circuit design is the need to fit large, generally rectangular or cylindrical components into a physiologically-shaped, curved housing. Of course, efforts are continually being made to minimize the size of the housing, and thus the size of the internal components, while maximizing the effectiveness of the device.
The control circuitry of implantable stimulation devices is often a multi-level hybrid circuit module. The multi-level module is ordinarily designed to achieve a low-volume configuration to facilitate placement within the limited confines of an associated device housing. Multi-level circuit modules may contain separate vertically stacked substrates, i.e., platforms, having individual circuit components mounted on the substrates. A protective cover, or lid, is typically placed over any exposed electronic circuitry of the multi-level module.
There have been many approaches documented in prior art publications for constructing a multi-layer, or three-dimensional, circuit module used in implantable devices. For example, in U.S. Pat. No. 5,222,014 issued to Lin, and Japanese publication No. 1-147850 issued to Kuwabara, independent circuit platforms are stacked above a substrate to create the multi-level structures. In each case a lid may be placed over the structure to protect the underlying circuitry.
As the electronic circuit modules of implantable medical devices become more complex and more densely configured, design constraints for closely configuring the associated electronic components become ever more significant. In particular, the electronic components must be free of errant particles and other ionic contaminants which could interfere with the electronic circuitry or damage miniature wirebond connections.
Some methods of sealing pacemaker devices and the like include those disclosed in U.S. Pat. No. 5,480,416 issued to Garcia et al., and U.S. Pat. No. 4,616,655 issued to Weinberg et al. In the Garcia et al. patent, an electrically insulative coating is applied over the entire surface of the implantable device case. In Weinberg et al., however, the electronic pulse generator of a cardiac pacer includes an internal chip carrier housing which is hermetically sealed.
In a high voltage system, such as an implantable cardioverter-defibrillator, the packaging density of the electronic components within an implantable device module is largely determined by the dielectric properties of the material separating the components. Previous methods of insulating electronic components have including using air as a natural dielectric, or as disclosed in the Lin patent, an encapsulating molding compound may be placed over the various electronic components for protection. Such methods achieve a certain level of dielectric breakdown protection which may not be suitable for the increased packaging density found in the most advanced implantable medical devices.
The present invention represents an improvement over previous implantable medical devices which allows for increased packaging density and improved protectability of internal electronic components.